The invention relates to a method to assemble a steam generator, whose tube walls form a gas pass and that are suspended in a boiler steel structure, as well as such a steam generator.
Large steam generators are large structures containing a substantial amount of material, and various methods have been suggested and are used to assemble them. For example, JP 04257602 A proposes an assembly method for steam generators in which crossbeams are provided in the boiler steel structure that extend outward so that hoistable platforms can be suspended on them to improve the efficiency and safety of assembling tube walls. Furthermore, the cited document discloses the simultaneous assembly of buckstays, internal components, and tube walls for different height zones and hoisting them into installation position as soon as the module is completed.
In addition, an assembly method is known from DE 690 00 992 T2 for a steam generator in which the boiler steel structure and an outer part of the boiler top main grid is erected first. Then the main beams are assembled on the boiler base as well as additional beams for the subsequent boiler top main grid that form a grid. The main beams of this grid then lie inside the subsequent boiler. The boiler top main grid formed in this manner is successively hoisted, and the boiler including the internal components, tube wall and buckstays are gradually lifted.
In this assembly method, boiler assembly can only begin after the boiler steel structure is already in place.
In U.S. Pat. No. 3,751,783, another steam generator is disclosed that is constructed as a tube wall boiler. The outer boiler steel structure bears internal components that are constructed on the boiler base after the boiler wall is erected, and then gradually hoisted and mounted there.
In this assembly procedure, the internal components can be assembled only after the boiler steel structure and boiler wall are finished.
In addition, DE 100 14 758 A1 discloses the simultaneous construction of the top boiler walls and internal components in the nearly finished boiler steel structure when constructing a steam generator. The top boiler walls are inserted by a crane from above through the still-open boiler top main grid into the boiler steel structure. During this process, the inner part of the boiler top main grid can be assembled on the boiler base and gradually hoisted, and then the internal components can be assembled. These are hoisted through the finished top part of the boiler wall by cable hoisting systems, and then the inner part of the boiler top main grid is connected to the outer part.
This system substantially accelerates the construction speed and hence shortens the construction time. However, the outer parts of the boiler top main grid are shifted far outside in order to lift the tube walls from above. Tie rods that are used to suspend the tube walls from the main beams of the boiler top main grid then sit on the brackets of the main beams. The resulting extra steel is 200 to 350 tons depending on the size of the boiler.